1. Field of the Invention
The present invention relates to an ink for printing on a game ball. More specifically, the present invention relates to an ink for dispensing from an inkjet printing machine onto a surface of a game ball.
2. Description of the Related Art
Inks that are used in ink jet printing commonly are water-based resins which contain dye as a coloring agent. Other types of inks, such as solvent-based (i.e., non-aqueous) formulations and ultraviolet (“UV”) curable inks, could be useful in ink jet printing if an appropriate viscosity and surface tension of the ink could be achieved as to be compatible with both the ink jet printing system and the golf ball surface. UV curable inks are quick-curing inks and therefore are advantageous for use in continuous-type processes in which subsequent treatment of an ink-printed substrate is involved. A number of UV curable inks are known. For example, U.S. Pat. No. 4,271,258 discloses a photopolymerizable ink composition containing acrylate resin, methacrylate monomer or oligomer, acrylate monomer or oligomer, photoinitator, and a particular type of an epoxy resin. U.S. Pat. No. 5,391,685 discloses a UV curable ink, having an isocyanate compound added thereto. U.S. Pat. No. 5,391,685 contends that the ink disclosed therein is particularly well suited for printing on slightly adhesive plastic bases, such as those made of polyoxymethylenes and polypropylenes.
Screen printing on spherical surfaces such as golf balls can be difficult. As a result, pad printing customarily is used for marking golf ball surfaces. However, many of the known UV curable inks are not well suited for pad printing due to difficulties in transferring the ink from a pad to a substrate. Furthermore, UV curable inks that can be pad printed have not been found suitable for use on golf balls. More specifically, when applied to a golf ball, these inks are not sufficiently durable (impact resistant) to withstand multiple blows by a golf club. It would be useful to obtain a highly durable UV curable ink which has favorable pad transfer properties when used for printing an indicia on a surface such as a curved and dimpled surface of a golf ball, and which provides an image having good durability.
Ink jet printing is commonly used to form multicolor images on paper for use in advertising materials, computer-generated photographs, etc. There are two fundamental types of ink jet printing: continuous and drop on demand. U.S. Pat. No. 5,623,001 describes the distinction between continuous and drop on demand ink jet printing. In continuous ink jet printing, a stream of ink drops is electrically charged and then deflected by an electrical field either directly or indirectly onto the substrate. In drop on demand ink jet printing, the ink supply is regulated by an actuator such as a piezoelectric actuator. The pressure produced by the actuation forces a droplet through a nozzle or nozzles onto the substrate.
It is known to print directly on a game ball surface using a continuous ink jet printer which relies on an electric charge to deliver droplets of ink to the game ball surface. (See JP 8322967-A, published Dec. 10, 1996 (Bridgestone) and JP 2128774-A, published May 17, 1990 (Bridgestone)).
Normally inkjet inks are composed of all monomers due to the need for a low viscosity such as 30 centipoise or less. However, monomers do not provide the necessary durability if the indicia is printed over the top surface of a game ball. The use of oligomers would give more durability, however, the viscosity of oligomers is in the thousands of centipoises.